v3.22.2.2
Cover Page - USD ($)
$ in Billions
 12 Months Ended
Sep. 30, 2022
Nov. 16, 2022
Mar. 31, 2022
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Sep. 30, 2022    
Current Fiscal Year End Date --09-30    
Document Transition Report false    
Entity File Number 001-38042    
Entity Registrant Name ARROWHEAD PHARMACEUTICALS, INC.    
Entity Incorporation State Country Code DE    
Entity Tax Identification Number 46-0408024    
City Area Code 626    
Local Phone Number 304-3400    
Entity Address, Address Line One 177 E. Colorado Blvd    
Entity Address, Address Line Two Suite 700    
Entity Address, City or Town Pasadena    
Entity Address, State or Province CA    
Entity Address, Postal Zip Code 91105    
Security12b Title Common Stock, $0.001 par value    
Trading Symbol ARWR    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Entity Shell Company false    
Entity Public Float     $ 4.1
Entity Common Stock Shares Outstanding   106,005,722  
Documents Incorporated by Reference Portions of the Definitive Proxy Statement to be filed for Arrowhead Pharmaceuticals Inc.’s 2023 Annual Meeting of Stockholders are incorporated by reference into Part III hereof.    
Document Fiscal Year Focus 2022    
Document Fiscal Period Focus FY    
Entity Central Index Key 0000879407    
Amendment Flag false